Method for float and sink mineral separation



2,821,303 METHOD FOR FLOAT AND SINK MINERAL SEPARATION Filed May 6, 1952 N. L. DAVIS Jan. 28, 1958 2 Sheets-Sheet 1 In ven for e25 on Z.flaaza N. L. DAVIS 2,821,303

METHOD FOR FLOAT AND SINK MI NERAL SEPARATION Jan. 28, 1958 2 Sheets-Sheet 2 Filed May 6. 1952 flizarieeys United ttes aten't 2,8213% Patented Jan. 28, 1955 METHOD FOR FLOAT AND SINK MINERAL SEPARATION Nelson L. Davis, Chicago, ill.

Application May 6, 1952, Serial No. 286,249

4 Claims. (Cl. 209-1725) My invention relates to improvements in method of sink and float mineral separation.

One object of the invention is to provide simplified, accurate and efiective means for maintaining constant the specific gravity, the viscosity and other characteristics of the parting liquid in a sink and float bath.

Other objects will appear from time to time throughout the specification and claims.

My invention is especially applicable to a system wherein a bath of sink and float medium or parting liquid is maintained at a specific gravity greater than that of some and less than that of other of the elements to be separated and wherein the medium comprises finely divided magnetically susceptible solids or media such as magnetite and the like in suspension in water. For convenience, I refer hereafter to the parting liquid as the medium and to the magnetically susceptible solids as magnetic media or media.

The specific gravity of the medium depends on the concentration of media therein. The media tend to sink in the bath under the influence of gravity. it is essential that the specific gravity of the bath be uniform from top to bottom. Such uniformity results from the upward movement of the medium at a rate approximating or preferably slightly higher than, the sink rate of the media, the medium circulating through the bath from supply at the bottom to withdrawal from the top. The rate of up- Ward movement must always be so low as to avoid any appreciable eflect on the material being separated, so that pure sink and float separation may take place without any appreciable upward current classification.

The material to be separated is fed to the bath, the heavy solids report to the bottom, the light solids float to the top and the separated sink and float solids are separately discharged from the bath with a substantial amount of medium. Such medium is drained from the solids and immediately, without further treatment, returned for recirculation through the bath.

After draining, some media, some water and some finely divided non-magnetic material will adhere to the separated solids. This is removed by rinsing, the rinse water is immediately passed through a magnetic separator, and the magnetic media in densified condition are discharged by the magnetic separator and are immediately returned without further treatment for recirculation through the bath. The magnetic separator tails, containing mostly nonmagnetic solids are deslimed to remove the non-magnetic material from the system. The deslimed water, with any magnetic media not recovered by the magnetic separator is reused for rinsing.

The material to be treated in the bath will always include particles of widely varying size and shape. The amount of media and water withdrawn from the bath circuit, adhering to the surface of these particles, will vary in consonance with the variation in total surface area of the particles. A continuous and prompt return of such media to the bath circuit, in a matter of seconds, is therefore essential to prevent appreciable change in the specific gravity of the bath.

The raw material fed to the bath will always carry with it some finely divided non-magnetic material, such as clay, shales that disintegrate into clay and other materials of very fine particle size, much of which will be transferred from the feed solids and remain in the bath. Such nonmagnetic material, if allowed to accumulate will change the viscosity and specific gravity of the medium and seriously interfere with proper sink and float separation.

I prevent such accumulation, by providing a bleed oflf duct between the bath and the rinsing circuits which separately withdraws some of the medium from the bath circuit and passes it through a magnetic separator, which will recover the magnetic media and return them immediately to the bath circuit. The non-magnetic material, together with the rinse water will continue through the rinsing circuit to a deslimer sump. There the non-magnetic material and some of the water will be discharged from the rinsing circuit.

While the separate withdrawal of some of the medium may take place at any desired point in the bath circuit, I preferably by-pass the bath and purge the medium. by the magnetic separator in the rinse water circuit. However, a second magnetic separator might be used. The bleed 01? will preferably be continuous though it might be intermittent.

Any magnetic media contained in the underflow slurrics from the deslimer sump return in closed circuit to again be used as rinse water and will again be subjected to the influence of the magnetic separator so as not to be lost from the system.

The media returned by the magnetic separator to the bath circuit will be demagnetized only when difficulties are experienced resulting from a tendency of the mediate to settle out of the bath at an abnormally high rate. Generally, demagnetization is neither necessary nor desirable.

The rinsing water is the underflow liquid from the deslimer sump. It is supplied to spill boxes for distribution, by a centrifugal pump. Close volumetric control cannot be obtained by using a throttling valve for either the inlet or the pressure side of a centrifugal pump. Pulsations caused by the impeller of such a pump, water being relatively incompressible, if transmitted in full intensity through the pump discharge would cause a surging effect, in the spill box, detrimental to proper rinsing. I provide, therefore a static head tank to receive the pump discharge. Gravity flow from the bottom of the tank to the spill box can be accurately controlled by a throttling valve. The pump discharges more liquid than is needed for rinsing and the excess overflows from the tank and is returned to the feed inlet well of the deslimer sump.

In order that the operator may maintain accurate control of the density of the medium, I provide an automatic, continuously operating dip tube density or specific gravity recording indicator through which some of the medium on its way to the bath is by-passed, the meter usually requiring more by-pass medium than is necessary for the bleed off. Valves regulate the flow to the magnetic separator and the direct return to the bath circuit.

My invention is illustrated more or less diagrammatically in the accompanying drawings, wherein Figure l is a diagrammatic side elevation of a system embodying my invention;

Figure 2 is a flow sheet of the system shown in Figure 1.

Like parts are indicated by like characters throughout the specification and drawings.

1 is a vessel adapted to contain a bath of float and sink medium. 2 is a chute through which raw solids, for example coal, are fed to the bath for separation therein. 3 is a screened chute divided by the partition 4 into separate sections for the receipt of sink and float solids discharged from the bath. The means for discharging these solids from the bath form no part of the present invention and are not illustrated except for the weir 34 over which the float solids are discharged with a substantial amount of the medium.

is a chute which receives the medium drained from the solids through the screen 3 and discharges it through the duct 6 for direct return to the medium storage sump 7. 8 is a mechanically operated screen divided by the partition 9 into sink and float sections corresponding to the chute 3. Fluid removed from both sink and float solids by the upstream portion of the screen 8 is directed by the hopper 55 to the duct 6 for direct return to the sump 7. 10 is a spill box to discharge rinsing water on the sink and float solids, the water passes through the screen 8 to the hopper 11, carrying with it media and nonmagnetic fines. 12 is a duct leading from the hopper 11 to the magnetic separator 13. Media recovered from the rinse water by the magnetic separator is discharged directly to the medium storage sump 7 through the hopper 15 which may have a demagnetizing coil therein. The tails from the magnetic separator are discharged through the hopper 16, duct 17, to the deslimer sump or decanter 18 through the feed inlet well 19. 20 is a delivery trough in adapted to receive the overflow including water and nonmagnetic fines from the deslimer sump for discharge from the system at 21.

The deslimer sump underflow is supplied by the pump 22 through the pipe 23 to the static pressure head tank a controlled amount of make up water to the hopper 7 in the bath circuit. The overflow from the standpipe 231 is returned by the pipe 235 to the deslimer sump 18.

2.4 is a duct adapted to receive the discharge of the medium storage sump 7 and supply it to the pump 25. The pump 25 discharges through the duct 26 to the valve 28 which controls the flow of medium through the expanding passage 29, and diffuser 30 to the bottom of the bath for upward flow therein just sufficient to maintain the density of the bath uniform. Duct 26 also supplies medium controlled by valve 31 through duct 32, difiuser 33 for discharge of medium at the top of the bath for cross flow toward the discharge weir 34.

35 is a valve adapted to be opened and closed by control means 36. When the valve 35 is closed and the valve 33, which is normally closed during operation, is opened,

is a valve by which fresh water may be supplied to the rinsing circuit in controlled amount to enable the deslimer sump to function properly as an upward current hydraulic classifier to eliminate slimes from the entire system and to furthermore serve the purpose of introducing any make up water necessary to replenish loss of water from the hydraulic system on the surfaces of the float and sink products.

is a pipe controlled by the valve 46 leading from the expanding passage 29 to the chamber of the density indicator 47. Medium flows thence through the pipe 48 to the pipe 12 on its way to the magnetic separator 13. The pipe 49 controlled by the valve 50 returns some of the medium directly to the medium sump 7.

The valve 46 controlling flow of medium to the chamber of the dip tube density indicator 47 must at minimum opening permit sufficient flow to prevent plugging of valve or pipe and at maximum flow must be sufiicient to permit purging of slimes from the bath circuit. The valves 46 and 51 may be manipulated to control flow to the density indicator to the magnetic separator and to the sump 7.

Referring to the flow sheet, Figure 2, the arrangement of the various circuits and the entire system is the same as in Figure 1. To avoid confusion, I have indicated flow and distribution by letter:

Fthe flow through the valve 234 of make up water from the rinsing circuit to the bath circuit.

G-the flow through valve 40 of make up water to the rinsing circuit.

H-the flow through pipe 21 for slime discharge from the system.

In order to provide effective rinsing B will always be a D will always be a variable because the. sizeand shape of the sink and float solids constantly change I and so constantly present difierent areas to which the.

constant.

liquid adheres as the solids and some of the liquid leave the system.

The slimes are brought into the system on the raw ma I terial fed to the bath and liquid and slimes leave the system with D and H. Therefore D +H=slime input Pumping water is expensive. Water is frequently hard to get and the water discharged from a plant such as this There" fore, special care must be taken to avoid wasteful use of,

must usually be clarified at substantial expense.

water. This can be done by maintaining the system balanced at all times so that only a minimum amount of water leaves the system and a minimum amount of make up is required.

The liquid leaving the bath circuit must be replacedbecause the bath circuit must itself be in balance. Therefore F must equal C plus D. Therefore F :C -[-D pensated for and therefore G =D +H Assuming that the bath circuit contains 3000 gallons of medium and that the flow at C from bath to magnetic 1 separator is 50 gallons per minute, then the entire volume of the bath circuit will run through the magnetic'separator This is enough to purge the bath circuit in an hour. of non-magnetic slimes.

The bath circuit loses not only 50 gallons at C but also 20 gallons per minute at D. This gallons per minute must be made up by 70 gallons at F.

netic separator to the deslimer sump. The pump 22 supplies the underfiow from the sump 18 to the standpipe 231. But since the standpipe 231 supplies not only 200 gallons. at B but also 70 gallons at F, the pump 22 must supply 270 gallons per minute to the standpipe 231.

For efiective desliming an overflow from the sump 18 i of 20 gallons per minute is needed so 20 gallons is lost.

to the entire system at D and 20 gallons at H. This is replaced by 40 gallons per minute of fresh water at G.

In view of the constant variation in the size and shape of sink and float particles, there will be a continuous variation in the loss at D but over any reasonable period of time, this averages out 'at 20 gallons per minute; There is also a permissible variation in the desliming overflow and so long as H averages 20 gallons per minute, desliming is satisfactory. If G flows continuously at 40 gallons per minute, then when D is greater than 20, H will be less and when D is less than 20, H will be greater.

The capacity of the pump 22 must in the interest of safety and because of gradual decrease of pump discharge as a result of wear be more than 270 gallons per minute. The excess will return at E from the standpipe 231 to the sump 18 and does not affect the balance of the system.

The magnetic separator is peculiar in that it is organized to work best on the thin slurn'es received from the rising screen and there bypassed from the bath circuit and it recovers and returns the magnetic media in such highly concentrated form to the bath circuit that for the purpose of the computations above indicated, the Water returned with the media to the bath circuit can be ignored. Some magnetic media will always be lost from the system, being carried out with the sink and float solids and on occasion it is possible, though it seldom happens, that some magnetic media might escape with the non-magnetic slimes. Such escape, however, will be very gradual, will show on the density indicator and the operator will be able to add make up media before any appreciable effect on operation occurs. Any evaporation of water will be so small that it also can be ignored.

Since raw material enters the bath continuously and sink and float solids are continuously discharged from the system, and since water and magnetite leave the system at two points only, namely-with the sink and float solids and with the decanted slimes and since make up is supplied to the system at one place only and since make up magnetite is supplied only to the bath circuit and since each of the two circuits and the relationship between the two circuits can be set for balanced operation, it will be seen that, once the various valves have been properly set, the whole system becomes automatic in its operation and little if any skill is required of the operator.

I have used, for brevity, the term rinsing circuit because rinsing of the sink and float solids takes place in that circuit. However, it is understood that the rinsing circuit has other functions, among them, the recovery of magnetic media for return to the bath circuit and the removal of non-magnetic slirnes for discharge from the entire system.

I claim:

1. The method of sink and float separation which consists in circulating a magnetically susceptible medium through a sink and float bath circuit, discharging sink and float solids and medium from the bath, draining the solids, returning the medium directly for recirculation in the circuit through the bath, rinsing the drained solids in a rinsing circuit, passing the rinsing water through a magnetic separating zone, returning the magnetically susceptible media recovered in the zone directly to the bath circuit, continuously withdrawing some of the medium from the bath circuit, passing such additional medium through a magnetic separating zone, returning directly to the bath circuit magnetically susceptible media recovered in said zone and discharging the magnetically unsusceptible solids in the additional medium withdrawn from the bath circuit for subsequent treatment.

2. The method of sink and float separation which consists in circulating a magnetically susceptible medium through a sink and float bath circuit, discharging sink and float solids and medium from the bath, draining the solids, returning the medium directly for recirculation in the circuit through the bath, rinsing the drained SOlids in a rinsing circuit, passing the rinsing water through a mag netic separating zone, returning the magnetically susceptible media recovered in the zone directly to the bath circuit, continuously withdrawing some of the medium from the bath circuit, passing such additional medium through a magnetic separating zone, returning directly to the bath circuit magnetically susceptible media recovered in said zone, adding the remainder of the liquid with non-magnetic fines to a rinse Wa ter circuit and desliming the circulating rinse water for the removal from the circuit of the non-magnetic slirnes.

3. The method of sink and float separation which consists in circulating a magnetically susceptible medium through a sink and fiOBlt bath circuit, discharging sink and float solids and medium from the bath, draining the solids, returning the medium directly for recirculation in the circuit through the bath, rinsing the drained solids in a rinsing circuit, passing the rinsing water through a magnetic separating zone, returning the magnetically susceptible media recovered in the zone directly to the bath circuit, continuously withdrawing some of the medium from lthe bath circuit, passing such additional medium through a magnetic separating zone, returning directly to the bath circuit magnetically susceptible media recovered in said zone, adding the remainder of the liquid with non-magnetic fines to a rinse water circuit and desliming the circulating rinse water for the removal from the circuit of the non-magnetic slimes, adding water from the rinse water circuit directly to the bath circuit to compensate for the liquid leaving the bath circuit.

4. The method of sink and float separation which consists in circulating a magnetically susceptible medium through a sink and float bath circuit, discharging sink and float solids and medium from the bath, draining [the solids, returning the meditun directly for recirculation in the circuit through the bath, rinsing the drained solids in a rinsing circuit, passing the rinsing water through a magnetic separating zone, returning the magnetically susceptible media recovered in the zone directly to the bath circuit, continuously withdrawing some of the medium from the bath circuit, passing such additional medium through a magnetic separating zone, returning directly to the bath circuit magnetically susceptible media recovered in said zone, adding the remainder of the liquid with nonmagnetic fines to a rinse water circuit and desliming the circulating rinse water for the removal from the circuit of the non-magnetic slimes, adding water from the rinse water circuit directly to the bath circuit to compensate for the liquid leaving the bath circuit, adding water to the rinsing circuit to compensate for the liquid leaving the system.

References Cited in the file of this patent UNITED STATES PATENTS 2,113,609 Wuensch Apr. 12, 1938 2,206,980 Wade July 9, 1940 2,325,149 Rakowsky et al July 27, 1943 2,373,635 Wuensch Apr. 10, 1945 2,387,866 Walker Oct. 30, 1945 2,496,590 Marsh Feb. 7, 1950 2,633,987 Bean Apr. 7, 1953 

